This invention relates to extruding devices and in particular to a new and useful apparatus for producing a helically wound thermoplastic tube. This invention relates to a device for the production of a pipe, a tube, a container having a cylindrical portion, or any partially cylindrical object (hereinafter referred to simply as "a tube") by the helical winding of a thermoplastic material having a profiled cross-section. This invention particularly relates to a method of production of such a tube in a single helical winding.
In prior art methods, a heated thermoplastic strip in the molten state is first helically wound on a heated rotating mandrel to produce a smooth tube by the welding together (fusion) of the abutting or overlapping edges of the molten thermoplastic strip in adjacent turns. This process, in itself, would produce a smooth cylindrical tube with a smooth interior surface upon removal from the mandrel. However, the tube would lack sufficient strength and rigidity for many uses when the tube diameter exceeds a few inches. It is known in the art that the tube can be reinforced with a tubular reinforcing member, or tubular rib, (preferably a thermoplastic material supported on a hose, more preferably a hose with a corrugated wall, and most preferably a corrugated polypropylene hose). The tubular reinforcing member is welded in the same or different helical period to the thermoplastic strip of the cylindrical tube. Such tubular ribs lend a characteristic cross-sectional profile to the finished tube, and are sometimes referred to as "profile sections".
The prior art has suggested that the thermoplastic strip and the tubular rib be simultaneously extruded as a single extrudate resembling a flanged tube and pressed upon the mandrel to form the cylindrical tube by welding adjacent flanges. In this vein, U.S. Pat. Nos. 4,466,854 and 4,510,004, the disclosures of which are herein incorporated by reference, disclose devices for the production of a tube by helical winding of thermoplastic extrudates having certain profile sections onto a mandrel. The prior art devices include a calibrated sliding profiled pressure member, or template, of a width at least corresponding to the width of the thermoplastic extrudate. The slide welds together the abutting or overlapping edges of the extrudate wound upon the mandrel. The slide is displaced along with the extruder in the axial direction of the rotating power-driven mandrel. The extrusion head provides a single continuous extruded thermoplastic extrudate of a profile section having two base flanges which form the longitudinal edges for welding, and also includes an outwardly projecting tubular reinforcement between the flanges which forms the tubular rib. The extrusion head is disposed with its longitudinal axis on a tangent to the mandrel corresponding to the pitch of the helix. The calibrated slide is disposed coaxially with the longitudinal axis of the extrusion head, has a guide channel for the outwardly projecting tubular reinforcement, and has internal passages through which a coolant passes to prevent sticking of the hot extrudate to the slide. It is of decisive significance according to the cited art that the extrudate be a single thermoplastic profile section, namely, having two base flanges for forming the longitudinal edges and an outwardly projecting longitudinal reinforcement between them. It is also of decisive importance in the cited art to advance the plastic extrudate between the extrusion head of the extruder and the calibrating slide along an exactly straight line with no sagging. This is accomplished by driving the mandrel at a peripheral speed somewhat greater than the extrusion speed and thus drawing the profile section through the calibrating slide. Purportedly, this is the only direct means of insuring that the physical and technical properties of the tube will remain within very tight tolerances.
U.S. Pat. No. 4,510,004 also provides a method for producing a reinforced tube of hollow profile section in which the plastic is deposited onto a rotating mandrel and at the same time a profiling material, such as a hose, is directed onto the plastic material and combined therewith without substantial tension. In this prior art method, there is purportedly no risk of deforming the tube. The extrudate is wound onto a mandrel, together with a profiling material paid out from a material feeder. The thermoplastic extrudate is fed from the nozzle of an extruder in a deformable state and onto the mandrel to produce an obliquely wound assembly welded at the joints between successive turns. The extruder nozzle is preceded by a feeder which draws the supporting profiling material from a source, such as a bobbin, and urges it into a nozzle. The method utilizes traction rollers providing at least one feeding channel for the profiling material or supporting hose and at least one of the traction rollers is power-driven.
While the prior art describes successful methods for the production of spirally wound thermoplastic tubes, the devices are cumbersome and ill-adapted for flexible production of tubes of various diameters and rigidity. It would be advantageous if tubes of different helical period and different profiles could be made from the same extruder means by changing the periodicity of a thermoplastic winding in a single-pass winding operation. This is not possible in the single-pass winding operations of the prior art without changing the extruder head means to provide thermoplastic extrudates of different width.